Method and equipment for manufacturing oriented electrical steel sheet

Abstract

The present invention provides a method for producing grain-oriented electrical steel sheet having a uniform texture along its entire length in the longitudinal direction when viewed as a hot-rolled coil unit and exhibiting minimal variation in magnetic properties. The method comprises the steps of hot-rolling a steel slab having a predetermined composition to produce a hot-rolled sheet, annealing the hot-rolled sheet to produce an annealed hot-rolled sheet, cold-rolling the annealed hot-rolled sheet once or twice or more with intermediate annealing to produce a cold-rolled sheet having a final thickness, and subjecting the cold-rolled sheet to a primary recrystallization annealing and a secondary recrystallization annealing. The cold-rolling is performed using a tandem rolling mill with a total reduction ratio of 80% or greater, and the rolling is performed using at least one stand of the tandem rolling mill at a reduction ratio of 30% or greater and a work roll bite temperature of T0°C. The work roll bite temperature at one or both of the leading and trailing ends of the annealed hot-rolled sheet is set to 70°C or higher and at least 10°C higher than the steel sheet temperature T0°C.

Description

Technical Field

[0001] The present invention relates to a method and equipment for manufacturing a grain-oriented electromagnetic steel sheet. Background Art

[0002] A grain-oriented electrical steel sheet is a steel sheet having excellent magnetic properties and having a crystal structure (Goss orientation) in which the <001> orientation, which is the easy magnetization axis of iron, is highly aligned in the rolling direction of the steel sheet.

[0003] In order to achieve such a high degree of orientation integration, for example, Patent Document 1 proposes a method of heat-treating (aging treatment) a steel sheet at a low temperature during cold rolling.

[0004] Patent Document 2 discloses a technique in which the cooling rate during hot-rolled sheet annealing or annealing before finish cold rolling (final cold rolling) is set to 30°C / s or higher, and further, an inter-pass aging treatment of 2 minutes or longer is performed two or more times during finish cold rolling at a steel sheet temperature of 150 to 300°C.

[0005] Patent Document 3 proposes a method of raising the temperature of a steel sheet to a high temperature during cold rolling (warm rolling).

[0006] These various technologies maintain the steel sheet at an appropriate temperature during cold rolling or between cold rolling passes, thereby fixing carbon (C) and nitrogen (N) as solid solution elements to dislocations introduced during rolling, inhibiting dislocation movement and inducing shear deformation, thereby improving the rolling texture. By using these technologies, the (111) fiber structure known as γ fibers ({111}<112>) is generally reduced in the primary recrystallization texture after cold rolling, resulting in an increase in the frequency of Gossian orientation. Such grain-oriented electrical steel sheets are manufactured by using a composition system containing Si at 4.5 mass% or less, forming inhibitors such as MnS, MnSe, and AlN, and utilizing the inhibitors to induce secondary recrystallization.

[0007] On the other hand, Patent Document 4 proposes a technique (inhibitor-free method) that enables secondary recrystallization even when no component forming an inhibitor is contained.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 50-16610

[0011] Patent Document 2: Japanese Patent Application Laid-Open No. 8-253816

[0012] Patent Document 3: Japanese Patent Application Laid-Open No. 1-215925

[0013] Patent Document 4: Japanese Patent Application Laid-Open No. 2000-129356 Summary of the Invention

[0014] The inhibitor-free method utilizes further purified steel to promote secondary recrystallization through texture control. This method eliminates the need for high-temperature billet heating, enabling low-cost production. However, since inhibitors cannot promote secondary recrystallization, more precise control of texture formation is required. In particular, in methods involving rolling at high pressures with reductions of 30% or more per pass, varying rolling process conditions significantly influence properties.

[0015] Furthermore, hot rolling is generally performed using slabs cast during steelmaking as units. Therefore, during hot rolling, the leading end is rolled without tension, and the rolling speed is often very slow. Meanwhile, the trailing end can maintain the same rolling speed as at the longitudinal center, but the resulting shape is non-rectangular, known as a fishtail. Furthermore, the trailing end spends more time waiting for rolling, causing the temperature to drop during this waiting period. Therefore, when observing the hot-rolled coil (hot-rolled coil) on a coil basis, the positions corresponding to the head and tail ends are unstable portions (generally, the portions corresponding to less than about 5% from the front end or tail end of the hot-rolled coil, taking the total length of the hot-rolled coil in the longitudinal direction as 100%). Compared to the stable portion including the corresponding position in the longitudinal direction (generally, the portion corresponding to about 5 to 95% from the front end of the hot-rolled coil, taking the total length of the hot-rolled coil in the longitudinal direction as 100%), the formation of α fibers (<110> fiber structure) that are difficult to recrystallize increases, which is not necessarily a preferred structure for texture formation.

[0016] On the other hand, in processes other than hot rolling, coils are typically welded together at the process entrance and continuously passed through, so the coils are uniformly treated along their length. As a result, the difference in texture between the unstable and stable areas created during hot rolling remains, potentially degrading the magnetic properties of the unstable areas.

[0017] This difference between the unstable and stable regions can be gradually reduced by increasing the number of steps, such as performing intermediate annealing and performing a second rolling pass. However, when microstructure formation is performed in a single rolling pass without intermediate annealing, magnetic property degradation in the unstable region is unavoidable. Furthermore, even with intermediate annealing, if the total reduction ratio in a single cold rolling pass is 80% or higher, microstructure formation is essentially performed in this single cold rolling pass, potentially leading to magnetic property degradation. This trend is particularly pronounced when rolling is performed with a reduction ratio of 30% or higher in a single pass.

[0018] Furthermore, when comparing cold rolling using a reversing mill with that using a tandem mill, magnetic property degradation is more common in the latter. Reversing mills are not continuous production lines, but rather process coils individually. The unstable portion becomes the unpressed portion (the portion of the coil wound on both sides that cannot be rolled) and is ultimately removed. On the other hand, tandem mills are continuous production lines, applying uniform processing along the length of the coil, allowing them to utilize the unstable portion, which, as mentioned above, is prone to magnetic property degradation.

[0019] An object of the present invention is to provide a method for producing a grain-oriented electrical steel sheet having a uniform texture over the entire length in the longitudinal direction when viewed as a hot-rolled coil unit and having small variations in magnetic properties, and an apparatus system that can be used for the method.

[0020] The present inventors have completed the present invention based on the fact that they can produce a good texture over the entire longitudinal length and reduce fluctuations in the magnetic properties of a grain-oriented electrical steel sheet by subjecting the unstable portion of a hot-rolled coil unit to a predetermined heat treatment in a tandem rolling mill.

[0021] [1] A method for manufacturing a grain-oriented electrical steel sheet, comprising the steps of hot-rolling a steel slab having the following composition to form a hot-rolled sheet, annealing the hot-rolled sheet to form an annealed hot-rolled sheet, cold-rolling the annealed hot-rolled sheet once or twice or more with intermediate annealing to form a cold-rolled sheet having a final thickness, and subjecting the cold-rolled sheet to primary recrystallization annealing and secondary recrystallization annealing; wherein the composition comprises, in mass%, C: 0.01-0.10%, Si: 2.0-4.5%, Mn: 0.01-0.5%, Al: less than 0.0100%, S: 0.0070% or less, Se: 0.0070% or less, N: 0.0050% or less, and O: 0.0050% or less, with the remainder being Fe and unavoidable impurities,

[0022] The total reduction ratio of at least one cold rolling is 80% or more, and it is carried out using a continuous rolling mill.

[0023] The rolling in at least one stand of the tandem mill is performed under the conditions of a reduction ratio of 30% or more and a bite temperature of the work rolls of the stand of the tandem mill of T0°C.

[0024] The bite temperature of the work rolls at one or both of the leading end and the trailing end of the hot-rolled annealed sheet is set to 70° C. or higher and 10° C. or higher than T0° C.

[0025] [2] The method for manufacturing a grain-oriented electrical steel sheet according to [1], wherein the bite temperature of the work rolls at one or both of the leading end and the trailing end of the hot-rolled annealed sheet is set to a temperature of 120°C or higher and 20°C or higher than T0°C.

[0026] [3] The method for manufacturing a grain-oriented electrical steel sheet according to [1] or [2] above, wherein the at least one stand is the first stand of the tandem rolling mill.

[0027] [4] The method for producing a grain-oriented electrical steel sheet according to any one of [1] to [3], wherein the rolling performed in at least one stand of the tandem rolling mill is performed at a strain rate of 65 s -1 The above conditions are carried out, wherein one or both of the front end and the tail end of the hot rolled annealed sheet are subjected to a strain rate of less than 65s -1 Rolling is carried out.

[0028] [5] The method for producing a grain-oriented electrical steel sheet according to any one of claims [1] to [4], wherein the steel billet further contains, in terms of mass%, one or more elements selected from the group consisting of Ni: 0.005-1.50%, Sn: 0.01-0.50%, Sb: 0.005-0.50%, Cu: 0.01-0.50%, Mo: 0.01-0.50%, P: 0.0050-0.50%, Cr: 0.01-1.50%, Nb: 0.0005-0.0200%, B: 0.0005-0.0200%, and Bi: 0.0005-0.0200%.

[0029] [6] An equipment train comprising a heating device and a continuous rolling mill, further comprising a detection device for detecting the position of a steel plate in the longitudinal direction and a control device for the heating device.

[0030] The control device controls the heating device based on the output from the detection device to adjust the bite temperature of the work rolls of at least one stand of the tandem rolling mill.

[0031] [7] The apparatus according to [6], wherein the heating device utilizes any one of induction heating, electric heating, or infrared heating.

[0032] According to the present invention, there is provided a method for producing a grain-oriented electrical steel sheet having a uniform texture over the entire length in the longitudinal direction when viewed per hot-rolled coil and having small variations in magnetic properties, and an apparatus system that can be used for the method. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a diagram showing the relationship between the strain rate of the first stand of the tandem rolling mill of Example 1 and the bite temperature of the work rolls of the stand. DETAILED DESCRIPTION

[0034] <Steel Billet>

[0035] The steel slab used in the production method of the present invention can be produced by a known production method. Examples of the production method include steelmaking-continuous casting, ingot casting-blowing and the like.

[0036] The chemical composition of the steel slab is as follows: Here, "%" in relation to the chemical composition means "mass %" unless otherwise specified.

[0037] C: 0.01~0.10%

[0038] C is an element necessary for improving rolling texture. If it is less than 0.01%, the amount of fine carbides necessary for texture improvement is too small and a sufficient effect cannot be obtained. If it exceeds 0.10%, decarburization becomes difficult.

[0039] Si: 2.0~4.5%

[0040] Si is an element that improves iron loss by increasing electrical resistance. If the content is less than 2.0%, this effect is insufficient, while if it exceeds 4.5%, cold rolling becomes extremely difficult.

[0041] Mn: 0.01~0.5%

[0042] Mn is an element useful in improving hot workability. If the content is less than 0.01%, the effect is insufficient, while if the content exceeds 0.5%, the primary recrystallization texture deteriorates, making it difficult to obtain secondary recrystallized grains that are highly concentrated in Goss orientation.

[0043] Al: less than 0.0100%, S: 0.0070% or less, Se: 0.0070% or less

[0044] The present invention's production method utilizes an inhibitor-free process, suppressing the inhibitor-forming elements Al, S, and Se to less than 0.0100% for Al, 0.0070% for S, and 0.0070% for Se, respectively. Excessive amounts of Al, S, and Se cause the coarsening of AlN, MnS, and MnSe during slab heating to cause a non-uniform primary recrystallization structure, hindering secondary recrystallization. The amounts of Al, S, and Se are preferably less than 0.0050% for Al, less than 0.0050% for S, and less than 0.0050% for Se, respectively. The amounts of Al, S, and Se can each be 0%.

[0045] N: 0.0050% or less

[0046] The amount of N is suppressed to 0.0050% or less to prevent the formation of Si nitride after purification annealing by acting as an inhibitor. The amount of N may be 0%.

[0047] O: 0.0050% or less

[0048] O may serve as an inhibitor-forming element. If the content exceeds 0.0050%, secondary recrystallization becomes difficult due to coarse oxides. Therefore, the content is suppressed to 0.0050% or less. The content of O may be 0%.

[0049] While the essential components and inhibitory components of the steel slab have been described above, the steel slab may appropriately contain one or two or more selected from the following elements.

[0050] Ni: 0.005~1.50%

[0051] Ni improves magnetic properties by increasing the uniformity of the hot-rolled sheet structure. When Ni is present, it can be 0.005% or more to achieve sufficient addition effects, but can be 1.50% or less to avoid deterioration of magnetic properties due to instability of secondary recrystallization.

[0052] Sn: 0.01~0.50%, Sb: 0.005~0.50%, Cu: 0.01~0.50%, Mo: 0.01~0.50%, P: 0.0050~0.5 0%, Cr: 0.01~1.50%, Nb: 0.0005~0.0200%, B: 0.0005~0.0200%, Bi: 0.0005~0.0200%

[0053] These elements are all effective in improving iron loss. When these elements are contained, they may be contained above their respective lower limits to achieve sufficient additive effects, and below their respective upper limits to ensure sufficient development of secondary recrystallized grains. Among these, Sn, Sb, Cu, Nb, B, and Bi are elements that can also be considered auxiliary inhibitors, and their inclusion exceeding the upper limits is not preferred.

[0054] The remainder of the composition of the steel slab is Fe and inevitable impurities.

[0055] Manufacturing Process

[0056] The manufacturing method of the present invention comprises the steps of hot-rolling a steel slab having the above-described composition to produce a hot-rolled sheet, annealing the hot-rolled sheet to produce an annealed hot-rolled sheet, cold-rolling the annealed hot-rolled sheet once or twice or more with intermediate annealing to produce a cold-rolled sheet having a final thickness, and subjecting the cold-rolled sheet to primary and secondary recrystallization annealing. Pickling may be performed before cold rolling.

[0057] The steel slab having the above-described composition is hot-rolled to produce a hot-rolled plate. The steel slab can be heated to a temperature of, for example, 1050°C or higher and less than 1300°C before hot rolling. The inhibitor components in the steel slab of the present invention are suppressed, resulting in complete solid solution, thus eliminating the need for high-temperature treatment at 1300°C or higher. Heating to 1300°C or higher may cause excessive crystallization, potentially leading to defects known as scabs, so heating to less than 1300°C is preferred. For smooth rolling of the steel slab, heating to 1050°C or higher is preferred.

[0058] Other hot rolling conditions are not particularly limited, and known conditions can be applied.

[0059] The obtained hot-rolled sheet is annealed to obtain a hot-rolled annealed sheet. In this case, the annealing conditions are not particularly limited, and known conditions can be applied.

[0060] The obtained hot-rolled annealed sheet is cold rolled. Cold rolling can be performed once or twice or more with intermediate annealing. In the manufacturing method of the present invention, at least one cold rolling is performed with a total reduction of 80% or more using a continuous rolling mill. Rolling with a total reduction of 80% or more is very advantageous in terms of being able to improve the integration of the texture and form a structure that is beneficial to the magnetic properties, but the difference in texture between the stable part and the unstable part tends to become larger. The object of the manufacturing method of the present invention includes such rolling. The total reduction is preferably 95% or less for the purpose of obtaining the {110}<001> oriented structure required for secondary recrystallization.

[0061] Conditions such as the reduction ratio and steel plate temperature in each stand of a tandem rolling mill can be set based on the desired steel plate properties, production volume, and the like. However, in the manufacturing method of the present invention, rolling in at least one stand is performed under conditions where the reduction ratio is 30% or greater and the work roll bite temperature of the stand is T0°C. Hereinafter, a stand adopting these conditions will also be referred to as a "prescribed stand."

[0062] The specified stand reduction ratio is not particularly limited as long as it is 30% or higher, but is preferably 32% or higher, and less than 55%, preferably 50% or lower. Thus, at a higher-than-usual single-stand reduction ratio, the present invention achieves a uniform texture across the entire longitudinal length, reducing variations in magnetic properties.

[0063] The bite temperature T0°C of the work rolls of the specified stand is not particularly limited and may be, for example, 30°C or higher. When the specified stand is a stand corresponding to the first pass of rolling, T0°C may be around ambient room temperature (25°C). For example, in rolling using lubricating oil, lubricity is improved, so it may be slightly higher than room temperature, preferably 45°C or higher. Temperature adjustment can be achieved, for example, by supplying heated lubricating oil (for example, lubricating oil heated to 45-70°C) to the steel plate, thereby increasing the temperature due to contact heat transfer. On the other hand, in order to differ from the heat treatment of the unstable portion, T0°C may be 120°C or lower, preferably 100°C or lower, and more preferably 90°C or lower.

[0064] Warm rolling is a known method for improving texture. However, most methods utilize the heat generated by normal warm rolling to raise the temperature of the steel sheet, and then perform low-temperature heat treatment (aging) between passes (between the last pass and the next). However, this method does not distinguish between stable and unstable areas, and uniformly heat treats the coil along its longitudinal direction, making it impossible to achieve texture uniformity.

[0065] In contrast, in the manufacturing method of the present invention, the rolling of the stable portion is carried out under the above-mentioned conditions in principle, and one or both, preferably both, of the bite temperature of the front end into the work roll (T1°C) and the bite temperature of the tail end of the hot-rolled annealed sheet into the work roll (T2°C) are exceptionally set to a temperature of 70°C or higher and 10°C or higher than T0°C to distinguish between the stable portion and the unstable portion, thereby reducing the difference in texture between the stable portion and the unstable portion.

[0066] If one or both of T1°C and T2°C is less than 70°C, the effect of the heat treatment cannot be fully achieved. Therefore, one or both of T1°C and T2°C should be set to 70°C or higher, preferably 120°C or higher. Alternatively, T1°C and T2°C can be set to 280°C or lower, preferably 250°C or lower. Within this range, even when lubricating oil is used for rolling, it is easier to maintain the appropriate viscosity of the lubricating oil.

[0067] If the temperature difference between one or both of T1°C and T2°C and T0°C is less than 10°C, it is difficult to reduce the difference in texture, so the temperature difference is 10°C or more, more preferably 20°C or more. In addition, the temperature difference can be 150°C or less, preferably 100°C or less. Usually, the properties guaranteed as a coil are performed at the part with the worst properties. Therefore, the different properties at the end will affect the property evaluation. In the present invention, the tissue homogenization of the entire length of the coil is achieved, so the tissue is uniform and the coil does not need to be slit, and it can be used directly. From this point of view, it is not preferred to set an excessively large temperature difference, and the temperature difference can be 150°C or less, preferably 100°C or less.

[0068] The designated stand among the multiple stands included in the tandem rolling mill may be one or two or more, and may be any of the multiple stands, but is preferably the first stand. Controlling the bite temperature of the work rolls in the first stand maintains this effect during rolling in subsequent stands, thereby achieving a favorable heat treatment effect.

[0069] The nip temperature of the work rolls of a predetermined stand can be controlled by combining a continuous rolling mill with a heating device and varying the heating of the coil in the continuous rolling mill according to the position of the coil in the longitudinal direction.

[0070] For example, the nip temperature can be controlled by increasing the output of the heating device at one or both of the leading and trailing ends in the longitudinal direction of the coil, while reducing the output (including shutting off the output) at other locations. Furthermore, if the ends of the hot-rolled coil are cut off in a previous step, the heating device control of the present application can be avoided at the ends of the coil.

[0071] The heating method of the heating device is not particularly limited. In order to change the bite temperature according to the position in the long side direction, it is preferred to directly heat the coil in the through plate for a short time. Considering the ability to heat up in a short time, induction heating, electric heating, infrared heating and other heating methods are preferred.

[0072] By further combining a detection device for detecting the position of the coil in the long side direction and a control device for the heating device, the bite temperature of the working roll of a specified frame can be adjusted by the heating device using the control device for the heating device based on the output from the detection device (position information in the long side direction).

[0073] Furthermore, in a predetermined stand, rolling at a reduced strain rate in the unstable portion is advantageous in reducing the difference in texture between the stable portion and the unstable portion. For example, the strain rate condition of the predetermined stand can be set to 65s. -1 Above, in the stable part with a strain rate of 65s -1 Rolling is performed, and the strain rate is exceptionally reduced at one or both of the leading end and the trailing end of the hot-rolled annealed sheet to less than 65s -1 Rolling is carried out.

[0074] Here, the strain velocity ε can be calculated using the following Ekelund formula,

[0075] [Mathematical formula 1]

[0076]

[0077] (Here, v Ris the roller peripheral speed (mm / s), R' is the roller radius (mm), h1 is the plate thickness on the roller inlet side (mm), and r is the reduction rate (%). ). The strain rate can be adjusted by changing the roller diameter, the plate passing speed during rolling (roller peripheral speed), etc. For example, by reducing the strain rate and extending the residence time in the heating device, the bite temperature can be easily increased, which is useful when the capacity of the heating device is insufficient. In addition, by referring to Japanese Patent Publication No. 2012-184497, at the stage where the total reduction rate is less than 50%, the strain rate is reduced to obtain the same effect as warm rolling, and the burden of heat treatment performed by the heating device can also be reduced.

[0078] The resulting cold-rolled sheet of the final thickness (also referred to as "final cold-rolled sheet") is subjected to primary recrystallization annealing and secondary recrystallization annealing to produce grain-oriented electrical steel sheet. After the primary recrystallization annealing of the final cold-rolled sheet, an annealing separator may be applied to the surface of the steel sheet before secondary recrystallization annealing.

[0079] The primary recrystallization annealing is not particularly limited and can be performed using a known method. The annealing separator is not particularly limited and a known annealing separator can be used. For example, an aqueous slurry containing magnesium as the main agent and additives such as TiO2 as needed can be used. Annealing separators containing silicon dioxide, aluminum dioxide, etc. can also be used.

[0080] There is no particular limitation on the secondary recrystallization annealing, and it can be performed using a known method. When a separator with magnesium as the main agent is used, a coating mainly composed of forsterite can be formed together with the secondary recrystallization. When a coating mainly composed of forsterite is not formed after the secondary recrystallization annealing, various additional steps such as a treatment for forming a new coating and a treatment for smoothing the surface can be performed. When forming an insulating coating with tension, the type of insulating coating is not particularly limited, and any of the known insulating coatings can be used. Preferably, a coating liquid containing phosphate-chromic acid-colloidal silica is applied to a steel plate and sintered at about 800°C. For these methods, for example, reference can be made to Japanese Patent Application Laid-Open No. 50-79442 and Japanese Patent Application Laid-Open No. 48-39338. In addition, the shape of the steel plate can be adjusted by flattening annealing, and flattening annealing that also serves as the firing of the insulating coating can be further performed.

[0081] Example

[0082] [Example 1]

[0083] A steel slab containing 0.04% C, 3.2% Si, 0.05% Mn, 0.005% Al, and 0.01% Sb, with S, Se, N, and O reduced to 50 ppm or less, and the remainder consisting of Fe and unavoidable impurities, was heated to 1150°C and hot-rolled to produce a 2.0 mm hot-rolled coil. The hot-rolled sheet was then annealed at 1035°C for 40 seconds. Subsequently, the sheet was cold-rolled to a thickness of 0.23 mm.

[0084] Cold rolling uses a continuous rolling mill equipped with an induction heating device before the first pass entrance of the rolling mill (roller diameter 4 stands), slowing down the rolling speed at the corresponding position of the head and tail ends of the coil, and using an induction heating device to control the bite temperature of the working rolls of the first stand of the rolling mill.

[0085] Figure 1 The figure shows the change in strain rate and work roll bite temperature of the first stand of a tandem mill. The horizontal axis represents the distance from the leading edge of the coil, with the leading edge being 0% and the trailing edge being 100%.

[0086] The specific controls are as follows.

[0087] The bite temperature of the front end of the coil is controlled at 120°C and the strain rate is 29s -1 Rolling under the conditions of .

[0088] Then, the bite temperature was 70℃ and the strain rate was 58s. -1 At the stage of the coil length in the long side direction of more than 5% and less than 95% of the stable part, the bite temperature is 60 ° C, the strain rate is 87s -1 Rolling under the conditions of .

[0089] The bite temperature of the tail end of the coil is controlled at 75℃ and the strain rate is 29s -1 The rolling was carried out under the conditions of .

[0090] The obtained cold-rolled sheet was subjected to primary recrystallization annealing at a soaking temperature of 800° C. and a soaking time of 120 seconds.

[0091] An annealing separator containing MgO as a main component was applied to the obtained primary recrystallization annealed sheet, and secondary recrystallization annealing was performed at a soaking temperature of 1150° C. for a soaking time of 7 hours.

[0092] The secondary recrystallization annealed sheet was coated with a coating solution containing phosphate and chromic acid and subjected to stress relief annealing at 850°C for 50 seconds. The maximum iron loss difference (ΔW) between the stable portion and the head and tail ends of the obtained steel sheet was 17 / 50 (W / kg)) is 0.013W / kg (worse at the head and tail ends).

[0093] For comparison, the strain rate was kept constant at 30°C for 58 s over the entire length. -1 The steel sheet was cold rolled and the maximum iron loss difference (ΔW 17 / 50 (W / kg)), the result is 0.022W / kg (the head and tail ends are worse).

[0094] [Example 2]

[0095] A steel slab containing, by mass%, C: 0.04%, Si: 3.1%, Mn: 0.06%, Al: 0.005%, Cr: 0.01%, P: 0.02%, S, Se, and O less than 50 ppm, N controlled to less than 40 ppm, and the remainder consisting of Fe and unavoidable impurities, was heated to 1180°C and hot-rolled into a hot-rolled coil with a thickness of 2.0 mm. The hot-rolled coil was then annealed at 1050°C for 60 seconds. The annealed hot-rolled coil was then rolled using a continuous rolling mill (roller diameter 1000 mm) equipped with an induction heating device before the first pass entrance of the rolling mill. 4 stands), pressed down to 0.26mm to make cold rolled sheet.

[0096] During the cold rolling, the strain rate and the nip temperature were changed for the leading and trailing ends and the stable portion of the coil as shown in Table 1. The reduction ratio of the first stand (first pass) was 32%.

[0097] The resulting cold-rolled sheets were subjected to primary recrystallization annealing with an average heating rate of 150°C between 50°C and 700°C, a soaking temperature of 800°C, and a soaking time of 50 seconds. Ten 30 mm x 30 mm test specimens were cut from the primary recrystallization-annealed sheets, each from the stable portion and the leading and trailing ends, and X-ray inverse intensity measurements were performed.

[0098] Next, an annealing separator containing MgO as a main component was applied to the primary recrystallization annealed sheet, and secondary recrystallization annealing was performed at a soaking temperature of 1200° C. for a soaking time of 5 hours.

[0099] The obtained secondary recrystallization annealed sheet was coated with a coating solution containing phosphate-chromate-colloidal silica in a weight ratio of 3:1:2. After stress relief annealing at 800°C for 3 hours, ten 30 mm × 280 mm test pieces were cut from the stable portion and the head and tail ends, and the iron loss W was measured according to the Epstein test. 17 / 50 (W / kg). The results are shown in Table 1.

[0100]

[0101] As shown in Table 1, in the examples of the invention, the variation in texture within the coil was suppressed, and the difference in magnetic properties was small.

[0102] [Example 3]

[0103] The steel slabs containing the components shown in Table 2 were heated to 1200°C and hot rolled to form 2.2 mm thick hot rolled coils. The hot rolled coils were then annealed at 950°C for 30 seconds. 4 stands) are pressed down to 0.22mm to make cold-rolled plates.

[0104] During the cold rolling, the strain rates at the leading and trailing ends of the coil and the stable portion were set to 62.7s -1 and 125.5s -1 In addition, the nip temperatures of the coil's leading and trailing ends and the stable portion were set to 120°C and 70°C, respectively, by a heating device with an induction heating coil disposed before the first pass entrance of the rolling mill.

[0105] The obtained cold-rolled sheet was subjected to primary recrystallization annealing at a temperature between 300° C. and 700° C. at a heating rate of 250° C. / s, a soaking temperature of 850° C., and a soaking time of 40 seconds.

[0106] An annealing separator containing MgO as a main component was applied to the primary recrystallization annealed sheet, and secondary recrystallization annealing was performed at a soaking temperature of 1200° C. for a soaking time of 5 hours.

[0107] The obtained secondary recrystallization annealed sheet was coated with a coating solution containing phosphate-chromate-colloidal silica in a weight ratio of 3:1:2. After flattening annealing at 850°C for 30 seconds, 30 mm × 280 mm test pieces were cut from the stable portion and the head and tail ends, respectively, with a total weight of 500 g or more. The iron loss W was measured by the Epstein test. 17 / 50 The results are shown in Table 2.

[0108]

[0109] As shown in Table 2, even when a steel billet containing an additive element is used, the same iron loss improvement effect is obtained.

Claims

1. A method for producing a grain-oriented electrical steel sheet, comprising the steps of hot-rolling a steel slab having the following composition to produce a hot-rolled sheet, annealing the hot-rolled sheet to produce an annealed hot-rolled sheet, cold-rolling the annealed hot-rolled sheet once or twice or more with intermediate annealing to produce a cold-rolled sheet having a final thickness, and subjecting the cold-rolled sheet to a primary recrystallization annealing and a secondary recrystallization annealing. The composition comprises, in mass%, C: 0.01-0.10%, Si: 2.0-4.5%, Mn: 0.01-0.5%, Al: less than 0.0100%, S: 0.0070% or less, Se: 0.0070% or less, N: 0.0050% or less, and O: 0.0050% or less, with the remainder being Fe and unavoidable impurities. The total reduction ratio of at least one cold rolling is 80% or more, and it is carried out using a continuous rolling mill. The rolling performed in at least one stand of the tandem rolling mill is performed under the conditions of a reduction ratio of 30% or more and a bite temperature of the work rolls of the stand of T0°C, in, The bite temperature of the work rolls at one or both of the leading end and the trailing end of the hot-rolled annealed sheet is set to 70°C or higher, and the bite temperature of the work rolls at the leading end and the trailing end of the hot-rolled annealed sheet is set to a temperature higher than T0°C by 10°C or higher. Here, the front end and the rear end correspond to being less than 5% from the front end side or the rear end side of the hot rolled annealed sheet, with the total length of the long side direction of the hot rolled annealed sheet being 100%.

2. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein: The bite temperature of the work rolls at one or both of the leading end and the trailing end of the hot-rolled annealed sheet is set to 120° C. or higher and 20° C. or higher than T0° C.

3. The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2, wherein: The at least one stand is the first stand of the tandem rolling mill.

4. The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 3, wherein: The rolling process performed in at least one stand of the continuous rolling mill is carried out at a strain rate of 65s -1 The hot rolled sheet annealing process is carried out under the above conditions, wherein one or both of the front end and the tail end of the hot rolled sheet annealing process is carried out at a strain rate of less than 65s -1 Rolling is carried out.

5. The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 4, wherein: The steel slab further contains, in terms of mass%, one or more elements selected from the group consisting of Ni: 0.005-1.50%, Sn: 0.01-0.50%, Sb: 0.005-0.50%, Cu: 0.01-0.50%, Mo: 0.01-0.50%, P: 0.0050-0.50%, Cr: 0.01-1.50%, Nb: 0.0005-0.0200%, B: 0.0005-0.0200% and Bi: 0.0005-0.0200%.

6. A plant train comprising a heating device and a tandem rolling mill, further comprising a detection device for detecting the position of a steel plate in the longitudinal direction and a control device for the heating device. The control device controls the heating device based on the output from the detection device to adjust the bite temperature of the work rolls of at least one stand in the tandem rolling mill. Under the condition that the bite temperature of the work rolls at the stable portion of the steel plate is T0°C, the heating device is controlled so that the bite temperature of the work rolls at the leading and trailing ends of the steel plate is 70°C or higher and 10°C or higher than T0°C. Here, the total length of the long side direction of the steel plate is set to 100%, the stabilizing portion corresponds to a portion that is more than 5% and less than 95% away from the front end side of the steel plate, and the front end and tail end correspond to less than 5% away from the front end side or the tail end side of the steel plate, respectively.

7. The device array according to claim 6, wherein: The heating device utilizes any one of induction heating, electric heating or infrared heating.

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